WASHINGTON (Reuters) – A pair of prominent Republican U.S. senators said on Sunday that the United States needs to prepare new sanctions against Russia to discourage interference in upcoming elections.

Senator Lindsey Graham said additional sanctions must be teed up before President Donald Trump holds a second meeting with Russian President Vladimir Putin after the U.S. leader came under heavy criticism for failing to confront Putin about interference in the 2016 election at a summit last Monday.

“You need to work with Congress to come up with new sanctions because Putin’s not getting the message,” Graham said on CBS’s “Face the Nation.” “We need new sanctions, heavy-handed sanctions, hanging over his head, and then meet with him.”

Undaunted by the backlash in his own party to his first meeting, Trump invited Putin to a White House meeting sometime this fall. Congressional midterm elections will take place in November.

Senator Marco Rubio wants a vote on a bill called DETER that would impose new sanctions if U.S. intelligence officials determine Russia meddled in U.S. elections. Rubio co-authored the legislation with Democratic Senator Chris Van Hollen, a bipartisan effort revived by the fallout of last week’s summit.

“What I think is indisputable is that they did interfere and they will do so in the future,” Rubio said on CNN’s “State of the Union.”

“If our bill passes and the director of national intelligence says they interfered in 2018, these very tough sanctions will hit them. So Putin knows going in, what the price of doing so is.”

Putin has denied that Russia tried to influence the 2016 presidential election after the U.S. intelligence community concluded Russia interfered through cyber attacks and social media in a bid to boost Trump’s candidacy.

Under pressure from Congress, which last year passed a tough sanctions law targeting Russia, the U.S. Treasury in April imposed sanctions on Russian officials and oligarchs for election meddling and “malign” activities.

The DETER Act would make sanctions more automatic. The U.S. director of national intelligence would be required to conclude if any foreign nations interfered in elections one month after Americans cast their votes, triggering strict sanctions within 10 days if interference was detected.

Senate Majority Leader Mitch McConnell last week identified the bill as a potential step Congress could take in the coming days to push back against Russia as Senate Minority Leader Chuck Schumer called for sanctions and other deterrents.

But the U.S. oil and gas industry is lobbying against the bill due to worries that heightened sanctions could impact U.S. investments in Russia, congressional sources said.